Traffic Engineering for Bit Index Explicit Replication (BIER-TE)
Gregory Cauchie, Michael Menth, Toerless Eckert · 2020
This memo introduces per-packet stateless strict and loose path steered replication and forwarding for Bit Index Explicit Replication packets (RFC8279). This is called BIER Tree Engineering (BIER-TE). BIER-TE can be used as a path steering mechanism in future Traffic Engineering solutions for BIER (BIER-TE). BIER-TE leverages RFC8279 and extends it with a new semantic for bits in the bitstring. BIER-TE can leverage BIER forwarding engines with little or no changes. In BIER, the BitPositions (BP) of the packets bitstring indicate BIER Forwarding Egress Routers (BFER), and hop-by-hop forwarding uses a Routing Underlay such as an IGP. In BIER-TE, BitPositions indicate adjacencies. The BIFT of each BFR are only populated with BPs that are adjacent to the BFR in the BIER- TE topology. The BIER-TE topology can consist of layer 2 or remote (routed) adjacencies. The BFR then replicates and forwards BIER packets to those adjacencies. This results in the aforementioned strict and loose path steering and replications. BIER-TE can co-exist with BIER forwarding in the same domain, for example by using separate BIER sub-domains. In the absence of routed adjacencies, BIER-TE does not require a BIER routing underlay, and can then be operated without requiring an Interior Gateway Routing protocol (IGP). BIER-TE operates without explicit in- network tree-state and carries the multicast distribution tree in the packet header. It can therefore be a good fit to support multicast path steering in Segment Routing (SR) networks.